One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the disk.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus, disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult using known technology to quickly and accurately position the read/write head over the desired information tracks on the storage media. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density.
One approach that has been effectively used by disk drive manufacturers to improve the positional control of read/write heads for higher density disks is to employ a secondary actuator, known as a micro-actuator, that works in conjunction with a primary actuator to enable quick and accurate positional control for the read/write head. Disk drives that incorporate a micro-actuator are known as dual-stage actuator systems.
Various dual-stage actuator systems have been developed in the past for the purpose of increasing the access speed and fine tuning the position of the read/write head over the desired tracks on high density storage media. Such dual-stage actuator systems typically include a primary voice-coil motor (VCM) actuator and a secondary micro-actuator, such as a PZT element micro-actuator. The VCM actuator is controlled by a servo control system that rotates the actuator arm that supports the read/write head to position the read/write head over the desired information track on the storage media. The PZT element micro-actuator is used in conjunction with the VCM actuator for the purpose of increasing the positioning access speed and fine tuning the exact position of the read/write head over the desired track. Thus, the VCM actuator makes larger adjustments to the position of the read/write head, while the PZT element micro-actuator makes smaller adjustments that fine tune the position of the read/write head relative to the storage media. In conjunction, the VCM actuator and the PZT element micro-actuator enable information to be efficiently and accurately written to and read from high density storage media.
One known type of micro-actuator incorporates PZT elements for causing fine positional adjustments of the read/write head. Such PZT micro-actuators include associated electronics that are operable to excite the PZT elements on the micro-actuator to selectively cause expansion or contraction thereof. The PZT micro-actuator is configured such that expansion or contraction of the PZT elements causes movement of the micro-actuator which, in turn, causes movement of the read/write head. This movement is used to make faster and finer adjustments to the position of the read/write head, as compared to a disk drive unit that uses only a VCM actuator. Exemplary PZT micro-actuators are disclosed in, for example, JP 2002-133803, entitled “Micro-actuator and HGA” and JP 2002-074871, entitled “Head Gimbal Assembly Equipped with Actuator for Fine Position, Disk Drive Equipped with Head Gimbals Assembly, and Manufacture Method for Head Gimbal Assembly.”
FIGS. 1 and 2 illustrate a conventional disk drive unit and show a magnetic disk 101 mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly (HGA) 100 that includes a micro-actuator 105 with a slider 103 incorporating a read/write head. A voice-coil motor (VCM) 115 is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider 103 to move from track to track across the surface of the disk 101, thereby enabling the read/write head to read data from or write data to the disk 101. In operation, a lift force is generated by the aerodynamic interaction between the slider 103, incorporating the read/write head, and the spinning magnetic disk 101. The lift force is opposed by equal and opposite spring forces applied by a suspension of the HGA 100 such that a predetermined flying height above the surface of the spinning disk 101 is maintained over a full radial stroke of the motor arm 104.
Because of the inherent tolerances of the VCM and the head suspension assembly, the slider 103 cannot achieve quick and fine position control which adversely impacts the ability of the read/write head to accurately read data from and write data to the disk. As a result, a PZT micro-actuator 105, as described above, is provided in order to improve the positional control of the slider and the read/write head. More particularly, the PZT micro-actuator 105 corrects the displacement of the slider 103 on a much smaller scale, as compared to the VCM, in order to compensate for the vibration or resonance tolerance of the VCM and/or head suspension assembly due to manufacturing tolerances. The micro-actuator 105 enables, for example, the use of a smaller recording track width, and can increase the “tracks-per-inch” (TPI) value by 50% for the disk drive unit, as well as provide an advantageous reduction in the head seeking and settling time. Thus, the PZT micro-actuator 105 enables the disk drive device to have a significant increase in the surface recording density of the information storage disks used therein.
FIGS. 3 and 4 illustrate a PZT micro-actuator disclosed in U.S. Patent Application Publication No. US 2003/0168935. As illustrated, a slider 133 (containing a read/write sensor) is partially mounted on a slider support 121 of the suspension 120. A bump 127 is formed on the slider support 121 to support the center of the back surface of the slider 133. A flex cable 122 including a plurality of traces is coupled to the slider support 121 and a metal base flexure part 123. A suspension load beam 124 with a gimbal 125 is provided to support the slider support 121 and flexure part 123. The gimbal 125 of the suspension load beam 124 supports the bump 127 of the slider support 121. This arrangement ensures that the load force from the load beam 124 is always applied to the center of the slider 133 when the slider 133 is flying on the disk.
Two thin-film PZT pieces 140, 142 are attached to the tongue region 128 of the flex cable 122 so that the thin-film PZT pieces 140, 142 are partially positioned under the slider 133. When a voltage is input to the two thin-film PZT pieces 140, 142, one of PZT pieces may contract C and the other PZT piece may expand E. This movement will generate a rotational torque T to the slider support 121. Since the slider 133 is partially mounted to the slider support 121 and the bump 127 of the slider support 121 supports the center of the slider 133, the slider 133 and the slider support 121 will rotate against the gimbal 125 of the suspension load beam 124.
Because the slider support 121 and-the load beam 124 are constructed from metal materials, the metal material of the bump 127 engages the metal material of the gimbal 125 and creates substantial rubbing between the bump 127 and the gimbal 125 in use. This rubbing will cause a reliability failure. Also, this rubbing will generate metal particles which may cause serious damage to the slider 133, the disk, or both, and therefore damage the disk drive unit. In addition, the rubbing will have a big effect on the head dynamic performance.
Another disadvantage of the prior design is the shock performance. Specifically, the slider 133 is partially mounted on the slider support 121, and the slider support 121 is coupled with the flexure part 123 by the flex cable 122. This arrangement provides very poor shock performance. As a result, the suspension 120 or thin-film PZT pieces 140, 142 may be damaged, e.g., crack or break, when a vibration or shock event occurs.
Thus, there is a need for an improved system that does not suffer from the above-mentioned drawbacks.